I have an idea for high traffic areas in cities where there are downward slopes. The idea is to add "buttons" on a downhill slope that when pushed by rolling vehicles will generate energy. The buttons will be made a certain size and distance apart in order to make the driver easy going about it. I do not have the exact plans for engineering these buttons, but I am not an engineer. I assume the energy can be used to power street lamps and signs. It is difficult to say how much energy will be produced or the cost of implimentation, but I think it can work very well.